Electronic device



Patented Nov. 23, 1948 ELECTRONIC DEVICE Ernest C. Okress, Montclair, N.J., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa.,a corporation of Pennsylvania Application August 28, 1945, Serial No.613,068 8 Claims. (Cl. 250 -275) This invention relates to electronicdevices and more particularly to magnetrons.

The magnetron has proved itself to be an exceedingly importantinstrumentality in the electronic art where used as an alternatingcurrent power generator, but has presented increasing difficulties inuse as a continuous-wave power source at high power levels. The troublearises largely from electronic bombardment of the cathode and consequentuncontrolled heating of the cathode. According to the present invention,solution of this problem is attained.

Broadly stated, then, an object of the invention is to provide anoperative continuous-wave magnetron having stable characteristics andlong life at high power output levels.

More specifically, an object of the invention is to provide a cathodecapable of being maintained at a controlled, reasonably constant anddesirable temperature during continuous operation.

Another object of the invention is to provide a cathode of desirablefeatures exterior to the resonant system such that adequate emission maybe obtained for high power output levels.

Of like nature, an object of the invention is to provide a structurefavorable to use of a cold cathode.

Another object of the invention is to adhere closely to symmetricalarrangement of anode and cathode with efficient electro-magneticcoupling from the generator to the external load.

A further object of the inventionis to incorporate a starting cathodesubstantially the same electron-path distance from the cavity resonatorsof the anode as the operating cathode.

Yet another object of the invention is to provide a magnetron structurehaving a. direct coaxial line output from the anode, coaxial therewith.

Other objects of the invention are to obtain a structure which ispractical from a manufacturing standpoint, which is simple in character,and which is of appropriate dimensions and configuration for efiicientand convenient use.

Still further objects of the invention will appear to those skilled inthe art to which it appertains, both by direct recitation thereof as thedescription proceeds and by implication from the context.

Referring to the accompanying drawing in which like numerals ofreference indicate similar parts throughout the several views;

Figure 1 is a longitudinal section on a diametric plane of a magnetronembodying the present 111-- vention; 1

Figure 2 is a CI'OSs section on line IIII of Figure 1; v

Figure 3 is an elevation of the starting cathode looking at the samefrom a sectional plane indicated by line III-III of Figure 1; and

Figure 4 is a sectional view similarto Figure 1 wherein liquid coolingis substituted for air cooling.

In the specific embodiment of the invention illustrated in said drawing,the reference numeral I0 designates a generally cylindrical anode with ahollow ll extending longitudinally and coaxially into one end (forconvenience of reference herein designated the upper end) ofa hubportion I2. Radia'lly around said hub portion, the anode provides acircular series of resonant cavities I3 here shown as each substantiallycylindrical open at both ends, axially parallel to the axis of the huband having a longitudinal slot 14 at the part thereof radially mostdistant from the axis of the hub. Segments or partitions l5,constituting parts of the anode, intervene in a circular series onebetween eachpair of cavities and slots. While a cavity resonator type ofanode is shown and described, a split plate anode may be substituted.

Gird'lin-g and spaced radially from the anode is 'i a cylindricalhousing It on the inner face of which is an emissive materialconstituting the cathode emitter l1. Preferably that material is formedas a band of less height than the cylindrical housing wall on which itis applied in radial opposition, so the top and bottom end margins ofsaid wall are free of emissive coating. Said band or emitter IT andcylindrical wall or housing I 6 together constitute the cathode. Saidemissive material is preferably of a characater ,whichwi'll copiouslyemit secondary electrons when bombarded by other electrons and is of thetype identified in the art as a "cold cathode. It operates atapproximately room temperature and with present known materials has theunfortunate characteristic of vaporizing or melting if raised to a hightemperature. Various cold cathode materials are available, such as asilver-magnesium mixture, another which is a nickelated compound,"

ameter of the anode in order that the anode may be introducedtherethrough in course of fabrication. The region bounded by saidcylindrical housing and by said end walls is termed the magnetronchamber,

At the bottom of the magnetron chamber as viewed in the arbitraryposition of the device as shown in the drawing, within the opening ofand coplanar with the washer-like end wall I8, is a disc-likesupplemental portion for the end wall I8 which has the anode mountedthereon. As shown, said anode has its hub portion [2 extended downwardto said supplemental end wall portion 20 which has a central hole intowhich a terminating reduced neck 2| of the hub is seated and soldered orotherwise made both rigid and vacuum tight. Said supplemental end wallportion 20 also constitutes the upper end closure for a tube 22 coaxialtherewith and with the anode, said tube having an exterior collar 23thereon at a lower part of itself and of appropriate material forsealing in the lower end of a glass ring 24 the upper margin of which isin turn sealed to a downwardly projecting edge of another collar'25depending from and soldered or otherwise secured to the anode housing.Supplemental end wall 20 is out of contact from the washer-like end walland, therefore, as to low potentials the tube and its end wall supportthe anode insulated from the cathode.

From a high frequency consideration, it is desirable to have acontinuous end wall for the cylindrical housing I 6. This desideratum isaccomplished in effect by providing a sleeve 26 around tube 22 inclosely spaced telescoped coaxial relation thereto, said sleevedepending from the inner periphery of the washer-like end wall l8 thedistance of a quarter wave length of the characteristic wave developedby the magnetron. The spacing between the tube and sleeve provides a gap21 the lower end of which is open at a quarter wave length distancebelow the plane of the end wall and therefore a high impedance is set upat the bottom or outer gap openin and a low impedance at the upper orinner gap opening.

This low impedance at the gap in the end wall of the magnetron chamberis equivalent, for high frequency, to a continuous wall.

A coaxial output coupling is provided from the upper end of themagnetron chamber. This coupling includes as part thereof an outertubular member 28 extending coaxially upward from the upper washer-likeend wall ill of the magnetron chamber. Said member is hollow, providin alarge cylindrical interior passage 29 next the outer end of the memberand a passage 30 which tapers from the large passage 29 down to thesmaller cylindrical hollow H in hub l2 of the anode, connecting theretowith a hollow neck 3|. Ex cept for said neck, the bottom of thetube isclosed and forms a supplemental end wall portion 32 to the washer-likeupper end wall ill of the magnetron chamber. The bottom of the tube isin the plane of the washer-like upper end wall 18 and is Within butspaced from the inner periphery thereof. As with the lower wall and tubeconstruction, the upper wall l8 has a sleeve 33 projecting .upwardlyfrom the inner periphery thereof a distance of a quarter wave length ofthe characteristic wave developed by the magnetron. The spacing betweenthe tube and sleeve provides a gap the upper end of which is open'at aquarter wave length distance above the plane of the end wall andtherefore a high impedance is set up at theupper gap openingthereof anda low impedance at the lower or inner gap opening. The low impedance atthe gap in the end wall of the magnetron chamber is equivalent, for highfrequency, to a continuous wall, and yet an insulative gap is providedagainst low frequency passage or applied D. C. voltage thereat.

Vacuum seal at the upper end of the magnetron chamber is obtained insimilar manner to the seal at the bottom of the chamber. The structurein detail provides an exterior collar 35 at an upper part of saidtubular outer member 28 of appropriate material for sealing in the uppermargin of a glass ring 36 the lower margin of which is in turn sealed toan upwardly projecting edge of another collar 31 projecting upwardlyfrom and soldered or otherwise secured vacuum tight to the anodehousing. By virtue of the glass ring 36 and gap 34, the coaxial outertube member 28 is out of contact with the anode housing and its upperend Wall, and therefore, as to low potentials said member and the anodeare insulated from each other.

vWithin and coaxial to the tube 28 and anode hub I2 is aninner'conductor 38 the diameter of which is proportionately larger inthe larger part 29 of the tubular outer member, tapering proportionately to smaller diameter in the tapered passage 30, and havingproportionately small diameter within the hollow ll of the'hub. A loop39 is located in one of the resonant cavities'l3 and has a stemextending radially inward, through a hole 40 in the hub, and connectswith said inner conductor 38. The hollow of the hub and outer coaxialtube 28 is evacuated, there being a glass seal 4| provided across thefar end of the tube between the inner surface thereof and the outersurface of inner conductor 38.

Beyond said glass seal'fll, the innerconductor isshown hollow andadapted to receive an expanding plug-like end 42 of another coaxialinnerconductor 43 representative of one section of an output line forthe device. This line also has an outer tubular conductor section 44,and preferably the inner and outer conductors 43- and 44 are ofcorresponding diameters to the inner and outer conductors respectivelyof the device .so as to form oontinuations thereof.

The outer tubular conductor 28 of the magnetron and the outer tubularconductor 44 of the output line preferably have their ends substantiallyabuttin and are mechanically coupled together. Such mechanical couplingis accomplished by employment of a releasable or separable structurepermitting attachment of the magnetron to any desired output line.

As here shown, tubular conductor 28 includes as part thereof and as theoutermost end, a length of material 45 to which the glass seal isparticularly capable of attachment and having a coefiicient of expansionsubstantially the same as the glass. metal seals shown in the drawingand referred to in the present description, a material and glass arepreferred such as described, in the patent to Howard Scott No.2,062,335, the material being sold in the market under the trade markKovar and the glass being a suitable borosilicate glass which isavailable as 704 Corning. The Kovar length 45 of the tube is shownsubstantially a quarter wave length with its outer end beyond theglassing and spaced with a small gap 46 from the end of the wave guideouter member. Depending from said wave guide outer member is a metallicsleeve 41 also of a quarter wave length depth surrounding and In theseveral instances of glass-to spaced by a cylindrical gap 48 from the"Kovar portion of the tube 28. This sleeve 41 provides a gap 49 at itslower end which opens into another cylindrical gap 50 on the outside ofsaid sleeve and within a second sleeve coaxial with and outside of thefirst said sleeve. Both of these sleeves 41 and 5| are shown dependingfrom a common ring 53 secured at the lower end of the wave guide outermember. The opposite or lower end of the second sleeve seats in anotherring 52 secured upon the outer cylindrical face of the magnetron tube28, said ring being so placed as to provide the aforementioned gap 46between it and the end of the inner or first mentioned sleeve 41. Itwill be understood that the tube 28, sleeves 41, 5| and rings 52, 53 areall metallic and conductive. It will be appreciated that as much of themetal surfaces exposed to high frequency are, whenever possible,preferably of as high conductivity material as possible, such as copperor silver. At the outside of the lower ring is secured a cylindricalhousing 54, spaced outward from and surrounding the second sleeve, theupper exterior margin of said housing being screw-threaded and receivingthereon the threaded flanged portion of a clamping cap 55 the headportion of which bears upon the outer flat end face of the wave guidering 53. Cap 55 and housing 54 clamp the second sleeve in a lengthwisedirection between the rings and thereby obtain a firm mechanicalassembly. The spacing of the inner sleeve by virtue of gaps 48, 49 and50 presents a half-wave length distance from the upper closed end of gap56 to the upper end of gap 48 where it opens into the gap 46 between themagnetron tube and the transmission outer member, thus presenting, as tohigh frequency, a low impedance at gap 46 and effect of electricalcontinuity from tube 45 to outer member 44 of the transmission line. Inorder for the magnetron to operate at certain desired region of itsimpedance plane which it sees at the base of the coupling loop 40, it isnecessary that a suitable transformer be inserted on the centerconductor 38 or the outer conductor 28 between the glass seal 4! and theloop 39 in vacuum to reduce high voltage break-down troubles.

The magnetron of the present showing is provided with ring-like magneticcoils 56 conveniently situated exterior to the magnetron body justbeyond the planes of the end walls 18, and by virtue of the magneticflux therefrom electrons emitted from cathode I1 tend to spiral. Withaid of the uniform actual magnetic field established by the coils 56over interaction space in which the electrons migrate between thecathode I6 and anode surface 10, plus the applied voltage between theanode and cathode, magnetron oscillations may be generated in theoperating region affected by voltage and magnetic field of proper valuefor the particular mode of operation, which in the present instancecrating temperature, I have shown in Figs. 1 and 2, an air cooledradiator comprising an inner shell 51 of substantially the length anddiameter of the cylindrical wall l6 of the magnetron and shrunk, brazed,soldered or otherwise held thereon in close contact for most effectiveheat conduction. At the outside of said shell 51 area plurality ofradiating fins 58 integral with the shell and separated from each otherand having appropriate surface area for dissipation of the desiredamount of heat to the surrounding atmosphere. A fan or other means forcirculating air through the radiator may be employed and may bethermostatically controlled by a thermostat either inside or outside ofthe magnetron. Anode cooling is obtained by conduction to tube 22 whichis hollow and open.

For adapting the invention to liquid cooling for even higher powerlevels than the air cooling, modification of Figure 4 may be employed.The magnetron structure of this liquid-cooled type is closely similar tothe air-cooled type and in general the same reference numerals apply.However, in the liquid-cooled type, the cathode emitter I1 is preferablycarried by a wall separate or distinct from the cylindrical housing wallof the magnetron. Thus, instead of coating the housing wall I6, Iprovide inward of and coaxial with said wall l6 another cylinder orcathode wall 59 on the inner face of which is applied secondary electronemissive material consisting emitter [1. 0n the outer face of saidcathode wall 59 away from the anode and toward the housing wall, butstill spaced therefrom, is a close fitting jacket 60 having a spiralfluid channel 6|. Feed and discharge pipes 62, 63 respectively connectwith opposite ends of said channel and extend through a side opening 64and are rigidly carried by a header 65 sealed by a glass ring to acollar 66 projecting from the opening and vacuum tight with respect tohousing cylinder I 6. The pipes constitute a supporting means for thecathode.

Water or other liquid cooling of the anode may be effected by provisionof a header 61 next the inner end of the hollow anode supporting tube 22as shown in Fig. 4. A liquid chamber 68 is formed between the header andthe end wall 20 of the tube so the fluid is indirect contact with thereduced end 2| of the anode hub. Inlet and outlet pipes 69, 10 for thefluid are secured to the header, opening into said chamber, and havingentry into said tube through the open end thereof. Rate of flow of theliquid may be controlled by a thermostat either within the magnetron orin or on the outlet pipe 10.

For instigating operation of the magnetron, a starting cathode 1| isprovided, this starting cathode being shown in Figures 1, 3 and 4 as ahairpin type of thermal electron emissive filament situated as nearly aspractical the same distance from the anode as the operating cathodeemitter l1 above described. The angular position of the filament withrespect to the gaps [4, especially in the case of the simple split-plateanode, must be such that a minimum back electronic bombardment isencountered. As shown, a conforming area 12 of the main cathode materialor emitter l1 has been omitted and the starting cathode situated thereatbut out of contact from the surface of the main cathode support. Lead-inwires 13 for the starting cathode 1| enter through a nipple 14 at theside of the cylindrical housing, the nipple having a collar 15 securedthereto and 7 capable of sealing to a glass stem 16 through which saidlead-in wires are sealed. A lateral tubulation TI is shown from theglass stem and by it the interior of the magnetron is evacuated and thetubulation pinched to a sealed condition for maintaining the vacuum.

I claim:

1. A magnetron device comprising a cylindrical housing having end walls,a sleeve of quarter wave length depth projecting outwardly from one ofsaid end walls, anode supporting means extending coaxially of saidsleeve and out of contact therefrom and having an end wall in the planeof said end wall of the housing having the sleeve, an anode mounted onsaid supporting means coaxially within the housing, and a cathodecoaxially around said anode and within the housing.

2. A magnetron device comprising a cylindrical housing having end walls,sleeves of quarter wave length depth projecting outwardly from said endwalls, anode supporting means extending coaxially of one of said sleevesand out of contact therefrom and having an end wall in the plane of oneof said end walls of the housing, an anode mounted on said end wall ofthe anode supporting means, a cathode coaxially around said anode andwithin the housing, and a coaxial output line having a tubular outermember extending coaxially through another of said sleeves, the saidtubular member having an end wall in the plane of the end of the housingfrom which the second mentioned sleeve extends.

3. A magnetron device comprising a cylindrical housing having end walls,sleeves of quarter wave length depth projecting outwardly from said endwalls, anode supporting means extending coaxially of one of said sleevesand out of contact therefrom and having an end wall in the plane of oneof said end walls of the housing having said one of said sleeves, ananode mounted on said end wall of the anode supporting means, a cathodecoaxially around said anode and within the housing, and a coaxial outputline having a tubular outer member extending coaxially through anotherof said sleeves, the said tubular member having an end wall in the planeof the end of the housing from which the second mentioned sleeve extendsand means sealing the said tubular member to the housing outside thesleeve thereat and sealing the said anode supporting means to thehousing outside the sleeve at that end of the housing.

4. A magnetron device comprising an anode, a secondary electron emissivecold cathode of greater diameter than and girdling the anode, means inheat conductive contact with the cathode at the side thereof away fromthe anode for dissipating heat from the cathode, and a starting cathodespaced from both the anode and the cold cathode, and said startingelectrode in its entirety being substantially the same distance fromsaid anode as said cold cathode.

5. A magnetron device comprising an anode, a secondary electron emissivecold cathode of greater diameter than and girdling the anode, means inheat conductive contact with the oathode at the side thereof away fromthe anode for dissipating heat from the cathode, and a thermionicstarting cathode spaced from both the anode and the cold cathode, andsaid starting electrode in its entirety being substantially the samedistance from said anode as said cold cathode.

6. A magnetron device comprising an anode, a secondary electron emissivecathode of greater diameter than and girdling the anode, said cathodeproviding a cold emitter as part thereof and providing means in heatconductive contact with the cold emitter at the side thereof away fromthe anode, means exterior to the first said means for transmitting anddissipating heat of conduction from the first said means by which saidemitter is kept at less than ruinous temperature, and a starting cathodespaced from both the anode and the cold emitter, and said startingelectrode in its entirety being substantially the same distance fromsaid anode as said cold cathode.

'7. A magnetron device comprising an anode, a secondary electronemissive cathode of greater diameter than and girdling the anode, saidcathode providing a cold emitter as part thereof and providing means inheat conductive contact with the cold emitter at the side thereof awayfrom the anode, means exterior to the first said means for transmittingand dissipating heat of conduction from the cold emitter by which saidemitter is kept at less than ruinous temperature, and a thermionicstarting cathode spaced from both the anode and the cold emitter, andsaid starting electrode in its entirety being substantially the samedistance from said anode as said cold cathode.

8. A magnetron device having an electron emitter and an anode with theemitter coaxial with and girdling the anode, a housing having acylindrical wall around said emitter and anode, said housing having endwalls at the ends of said cylindrical wall, means supporting the anodethrough one end wall physically out of contact from the same, and acoaxial output tube extending through the other end wall physically outof contact therefrom.

ERNEST C. OKRESS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,143,327 Snook et a1 June 15,1915 1,605,001 Schroter Nov. 2, 1926 1,963,168 Knowles June 19, 19342,108,900 Peterson Feb. 22, 1938 2,150,317 Clark Mar. 14, 1939 2,163,157Samuel June 20, 1939 2,289,984 Mouromtseff et al. 1 July 14, 19422,404,212 Bondley July 16, 1945 2,414,085 Hartman Jan. 14, 1947 FOREIGNPATENTS Number Country Date 229,019 Great Britain Feb. 19, 1925 298,804Germany Sept. 13, 1919 515,229 Great Britain Nov. 29, 1939

